Dr. D. DATTA Ex Emergency Medical Officer.
Read time: 5 minutes.
There are more than 3500 species of snakes in the world. Among them 250 species are venomous.
In India there are more than 250 species of snakes, of which about 60 species are venomous. Out of 60 venomous snake species in India 50 species are sea snakes.
In India 4 species are responsible for 99% of venomous snake bites. They are called BIG FOURS. Big fours are
1) Spectacle cobra (Naja naja).
2) Russell’s viper ( Daboia russelli )
3) Common krait ( Bungarus caeruleus ) and
4) Saw scaled viper ( Echis carinatus ).
Though saw scaled vipers are responsible for 75% venomous snake bites in India they are not found in the state West Bengal.
Snakes can be divided according to the main toxic component present in their venom
1) NEUROTOXIC – ( Cobra, Kraits, Coral snakes ) Their venom contains Neurotoxins
2) HEMATOTOXIC- ( Vipers, Pit Vipers ) Their venom contains Hemotoxins and
3) MYOTOXIC- ( All flat tailed Sea snakes ) Their Venom contains Myotoxins.
Snakes may also be divided according to the family they belongs to, such as
A) ELAPIDAE
B) VIPERIDAE and
C) COLUBRIDAE.
ELAPIDAE –
There are 300 species of snakes in this family. Members of this family are known as ELAPID.
Elapids are usually long, thin, mostly uniformed colored. They have large smooth symmetrical scales on the top of their head. Upper jaw contains paired fangs. The fangs are permanently erect. When the mouth is closed, fangs are covered by the lip outside the lower mandible.
Their venom contains mainly neurotoxins. Venom glands are situated below and behind the eyes on each side. from the venom gland a duct comes up to the base of tubular fangs. A groove is Present in each fang which is like a hypodermic needle through which Venom is injected.
Elapids are subdivided into two subfamily
1) Elapinae- It includes Cobra ( such as Spectacle cobra, Indian monocled cobra, King cobra), Kraits ( such as common Krait, Banded Krait, Wall’s Krait), Mamba and Coral snakes.
2) Hydrophiinae- Sea Kraits.
Three species of ELAPID snakes can spit their venom towards the eyes of a predator. Spitted venom may reach up to a distance of 3 Meters and may cause blindness if not washed immediately. This Venom contains more cytotoxins than neurotoxins.They are
1) Spitting cobra of South Asia ( Hemachatus haemachatus ).
2) African black necked cobra ( Naja nigricollis ) and
3) a subspecies of Asian cobra ( Naja Naja sputatrix ).
Cobras can extend the neck ribs to produce hood.
Most elapids are oviparous (producing eggs that develop and hatch outside the maternal body ). Some are ovoviviparous ( producing eggs that develop within the maternal body and hatch within or immediately after release from the mother’s body ). Some are viviparous (embryo is developed within the body eventually leading to giving birth to young rather than producing eggs ).
VIPERIDAE-
There are about 250 species of snakes in the Viperidae family. Members of this family are known as viperids.
Viperids are thick bodied, short tailed and have many small rough scales on the top of their head. They have a characteristic pattern of colored markings on their back. They have a triangular shaped head that is distinct from the body.
They have a pair of long hollow fangs at the front of the mouth on a maxilla that can rotate back and forth. The fangs can be folded back against the top of the mouth. Venom glands are situated below and behind the eyes on each side. From the venom gland a duct comes up to the base of tubular fangs. A groove is Present in each fang which is like a hypodermic needle through which Venom is injected.
Their venom contains mainly hemotoxins. Some of them may also contain neurotoxin such as Russells viper.
Viperids are divided into four subfamily
1) Viperinae- members are known as vipers ( such as Russell’s viper, saw scaled viper )
2) Crotalinae- members are known as pit vipers ( such as Hump nosed pit viper, Green pit viper, Mountain pit viper)
3) Causinae- e.g Night adders and
4) Azemiopinae.
Pit vipers need special mention. They are easily recognised by the presence of heat sensitive pit one on each side of head between the eyes and nostril. It is a special infrared heat sensing organ to detect warm-blooded prey.
COLUBRIDAE-
family colubridae has approximately 1760 species. It is the largest snake family (almost â…” of all snake species). Members of this family are known as Colubrids.
Some colubrid snakes are – Indian rat snakes, racers, garter snakes, grass snakes, king snakes, corn snakes, water snakes, green whip snakes, ring necked snakes, flying snakes etc.
Colubrids have grooved teeth situated at the rear extremity of maxilla. Venoms secreted by supralabial venom glands tracks down the groove in the anterior surface of fangs which is not totally covered. As their fangs are situated posteriorly to inject venom, prey is to be introduced deep in the mouth.
Most colubridae are non venomous but some may cause human fatalities such as
a) Boomslang ( Dispholidus typus ) it’s venom is primarily hemotoxin,
b) Twig snake ( Thelotornis spp.) commonly known as bird snake or vine snake. It’s venom is mainly hemotoxin.
c) Genus Boiga – known as cat snake or cat eyed snake or mangrove snake.
d) Genus Rhabdophis (Rhabdophis subminiatus)- commonly known as keelback is highly venomous.
Signs and symptoms of snake bite, Read more
The Lethality of Snake Venom: Toxic Compounds Explained, Read more
